Process for controlling position of electrode in electroslag remelting mold

ABSTRACT

A process for the refining of metals in which a consumable electrode of the metal to be refined is melted in a vessel which comprises detecting changes in the clearance between posed surfaces of the consumable electrode and the vessel inner wall to produce a control signal to impart relative horizontal movement between the electrode and the vessel to restore the clearance.

United States Patent [191 Hoyle PROCESS FOR CONTROLLING POSITION OFELECTRODE IN ELECTROSLAG REMELTING MOLD [75] Inventor: Geoffrey I-Ioyle,Sheffield, England [73] Assignee: The British Iron and Steel ResearchAssociation, London, England [22] Filed: May 10, 1972 [21] Appl. No.:251,888

[30] Foreign Application Priority Data 164/156; 13/1; 33/180 R, 181 R;318/625, 652, 324/34 R', 34 E [451 Apr. 16, 1974 3/1966 Speer 33/189 XFOREIGN PATENTS OR APPLICATIONS 1,103,350 2/1968 Great Britain 164/252Primary Examiner-J. Spencer Overholser Assistant Examiner-John E.Roethel Attorney, Agent, or Firm-Brisebois & Kruger [5 7] ABSTRACT Aprocess for the refining of metals in which a consumable electrode ofthe metal to be refined is melted in'a vessel which comprises detectingchanges in the clearance between posed surfaces of the consumableelectrode and the vessel inner wall to produce a con- 'trol signal toimpart relative horizontal movement between the electrodeand the vesselto restore the clearance.

3 Claims, 8 Drawing Figures [56] References Cited UNITED STATES PATENTS3,405,219 10/1968 Sivet 13/1 I 2 i H m;

i 8'-\ v x 1" PATENTEDAPR 16 IBM SHEET 1 UF 4 PATENTEH PR 16191 1 78,804,146 SHEET 2 OF 4 Md 72d PATENTED APR 16 I974 SHEET 3 BF 4 I l V AVThe present invention relates to apparatus and processes for therefining of metals and, more especially, to the secondary refining ofmetals.

Electroslag refining and vacuum arc remelting are examples of suchprocesses. In the electroslag refining process, a slag within a mould ismaintained in a molten state and at a temperature above the meltingpoint of the metal to be refined. Unrefined metal is introduced into themould and is refined as it passes in droplet form through a bath of themolten slag, refined droplets collecting to form a pool beneath the slagbath. The mould walls and base plate are cooled by the circulation of acoolant, normally water, and a solidified ingot I is built up beneaththe molten metal pool. The metal to be refined may be introduced to themould in the form of a consumable electrode and the slag maintainedmolten by passage of an electric current from the electrode to the baseplate. of the mould.

To prevent excessive heat loss in the electroslag refining process theclearance between the inner side wall of the mould and the surface ofthe consumable elec-' trode should not be excessive. To avoid damage tothe mould wall, contact between the opposed surfaces of the mould andthe electrode should be prevented.

In accordance with one aspect of the invention, a process for therefining of metals in which a consumable electrode of the metal to berefined is melted in a vessel, such as a mould, comprises detectingchanges in the clearance between opposed surfaces of the consumableelectrode and the vessel inner wall to produce a control signal toimpart-relative horizontal movement between the electrode and the vesselto restore the clearance.

Reductions in the clearance may be detected by three or moreelectrically activated probes which are spaced evenly around and extendinwardly from the vessel inner wall to define the desired minimumclearance between the vessel inner wall and the electrode and which areactivated by contact with the electrode. Activation of one probe or oftwo adjacent probes may cause a control signal or signals to be passedto drive means operable to impart relative horizontal movement betweenthe electrode and the vessel. The drivemeans may comprise electricalmotors each connected to receive a signal from one of the probes andeach operable to impart relative movement between the electrode and thevessel in such a horizontal direction as to de-activate the probe towhich a respective motor is connected. Each probe may be movable towardsand away from the electrode.

In accordance with another aspect of the invention, there is provided aprocess for the refining of metals in which a consumable electrode ofthe metal to be refined is positioned in a predetermined spacedrelationship to a mould, the process including the steps of detectingany relative movement in a horizontal direction between the electrodeand the mould, producing a signal indicative of the direction and extentof said relative movement and using said signal to operate one or moremotors to cause relative movement between the electrode and the mould toreturn the electrode and mould to the predetermined spaced relationship.

In accordance with a further aspect of the invention, apparatus for therefining of metals comprises an electrode and means to locate theelectrode in a'predetermined spaced relationship to a vessel, such as amould, the apparatus including means to detect departure from saidpredetermined spaced relationship and means to cause relative movementbetween the vessel .and the electrode so as to restore saidrelationship. The

means to detect departure from said relationship may comprise sensingprobes adapted to be contacted by the electrode and thus to set upelectrical signal to operate electrical motors arranged to causerelative movement between the electrode and the vessel. Four electricmotors may be spaced around the periphery of a trolley carrying thevessel, ,the motors being so arranged that one pair of motors will movethe trolley in one direction and the other pair of motors will move thetrolley in a direction at right angles to said one direction.

In accordance with a still further aspect of the invention, apparatusfor the refining of metals comprises a mould, means for mounting aconsumable electrode therein, three or more electrically activatedprobes Spaced evenly around and extending inwardly from the inner wallof the mould to define the desired minimum clearance between the mouldinner wall and the electrode when in position, and drive means connectedto receive signals from the, probes when activated by contact with theelectrode and operable to impart relative movement between the mould andthe electrode to move the probes out of contact with the electrode.

In the accompanying diagrammatic drawings,

FIG. 1 is an elevational view, partly in section, of electroslagrefining apparatus embodying the invention;

FIG. 2 is an underneath plan view of the trolley illustrated in FIG. 1;

FIG. 3 is a section in the line III-III of FIG. '1 to an enlarged scale;

FIG. 4 is a plan view of a detail of electroslag refining apparatusembodying the invention;

FIG. 5 is a section in the line V--V of FIG. 4;

- FIG. 6 is a view similar to FIG. 1 showing the electroslag refiningapparatus in a modified embodiment; and

FIGS. 7 and 8 are, respectively, plan and elevational views of furtherelectroslag refining apparatus embodying the invention.

In FIGS. I to 3, apparatus for the electroslag refining of metalincludes an open-ended mould 1 supported by a carriage 2 movablevertically relatively to a mast 3. A consumable electrode 4 is clampedin an electrode holder 5 which is movable vertically relative to a mast6. Initially, the mould is mounted on but insulated from a cooled baseplate 7. As the refining process proceeds an ingot is built up on thebase plate 7 and the carriage 2 raised so that the base plate 7 supportsthe formed ingot 8'. The base plate 7 and mast 3 are mounted on atrolley 9 movable in horizontal directions by electrical motors, e.g.Servomotors, 10a to 10d (FIGS. 2 and 3). Servomotors 10a to 10d are,respectively, operable to move the trolley 9 in the directions indicatedby arrows 11a to 11d. The electrode 4 and the base plate 7 are connectedto a source of alternating current. The slag bath and metal pool areindicated, respectively, at 13a and 13b. I

Sensing probes 12a, 12b, 12c, 12d are evenly spaced around the upperopen end of the mould land together define the desired clearance betweenthe electrode and the inner mould wall.

The probes 12a, 12b, 12c, 12d are, respectively, connected to relays14a, 14b, 14c, 14d which, when actuated, energise the respectiveservomotors a, 10b, 10c, 10d.

In operation, droplets of unrefined metal pass from the electrode 4 andcollect in a pool below the electrically conductive refining slag. Thesedroplets solidify to form the ingot 8. As the ingot builds up, the mould1 is raised by the carriage 2 to maintain a predetermined distancebetween the level of the molten metal pool 13b and the lower open-end ofthe mould. Due to irregularities in the surface of the consumableelectrode or to misalignment of the electrode relative to the mould,movement of the mould relative to the electrode may cause the clearancebetween the electrode and an adjacent surface of the'mould inner wall tobecome less than the predetermined distance. In this event, one or twoadjacent probes 12a 12d are contacted by and receive a voltage signalfrom the electrode, which signal actuates the corresponding relay orrelays 14a 14d to energise the corresponding servomotor or servomotors10a 10d. The servomotor(s) operates to move the trolley 9and,-consequently, the mast 3 and the mould l in such a direction thatthe activated probes 12 a 12d are moved out of contact with the adjacentelectrode surface. When contact between the probe(s) and the electrodeis severed, the motor(s) is or are deenergised and movement of thetrolley 9 is stopped.

A second array of probes 18a to 18d (FIG. 3) may be provided to allowfor regular increases in electrode cross section. If such an increaseshould occur, all four probes 12a to 12d are simultaneously energised,

whereupon they are all retracted by a motor (not shown) to positionsadjacent the mould inner wall. The minimum permissible clearance betweenthe electrode and the mould inner wall is now defined by probes 18a to18d, which probes are spaced evenly around and fixed to the mould upperend. In an alternative arrangement, the probes are in contact with theelectrode. Once this position has been reached, the motor retracting theprobes is switched off andthe respective servomotorsoperated to re-alignthe mould relative to the electrode until all of the probes 12 arede-energised. As previously described with reference to probes 12a to12d, should the electrode 4 contact one or two adjacent probes 18a to18d, the corresponding servomotor or servomotors 10a to 10d is or areoperated to move the trolley 9 and, consequently, the mould l to aposition in which an even clearance exists between the electrode and themould. However, should more than two probes 18a to 18d be activated atany one time, a switch is thrown to sound an alarm and/or to switch offthe melt power and the electrode drive.

The position of each probe 12a 12d may be externally adjustable relativeto the mould. That is to say, each probe may be moved towards and awayfrom the electrode during a melt to accommodate general variations inelectrode cross section. As illustrated in FIGS. 4 and 5, each probe 12has a screw-threaded portion 19 which co-operates with aninternally-threaded sleeve mounted on a collar 21 supported on the upperend of the mould wall. The probes may beextended periodic'ally towardsthe electrode until they make contact with it and the distances movedrecorded to give readings of the ratio of electrode to mould diameter.

Each probe may extend inwardly from the mould inner wall and three ormore probes may be employed. For example, eight evenly spaced probes maybe employed, each'probe being connected through a relay to a servomotor.

In the embodiment illustrated in FIG. 6, the mast 6 is movable inhorizontal directions by the motors 10a to 10d, the mast 3 and baseplate 7 being immobile. In this embodiment, contact of the electrodewith one or two of the probes 12a 12d or 18a 18d causes energisation ofthe servomotor(s) 10a to move the mast 6 and, consequently, theelectrode 4 in such a direction that the activated probes are moved outof contact with the adjacent electrode surface.

In the embodiment illustrated in FIGS. 7 and 8 the position of theelectrode 4 within the mould l is sensed by means of four pivotableprobes 20 which bear against the adjacent surface of the electrode 4.Each probe 20 is connected by an arm 21 to a member 22 which pivots withthe respective probe 20. The members 22 connected to opposed probes 20are interconnected by means of pivotally mounted links 23, 24 which areurged together by a spring 25. The links 23, 24 are coupled by an arm 26which carries a rod 27 which is movable vertically within a bearing 28and which can move sideways into contact with switches 29, 30. Theswitches, when actuated, energise respective servomotors operable tomove the mould 1 in a similar manner to the servomotors 10a 10dhereinbefore described.

In this embodiment, misalignment of the electrode causes the probes 20and the respective members 22 to pivot, thus moving one or both of therods 27 to one side to make contact with and actuate either switch 29 orswitch 30. Actuation of switch 29 or switch 30 energises the respectiveservomotors to move the mould 1 in such a direction that the pivotedprobes are returned to their original positions. When the probes havereturned to their original positions, each rod 27 is moved to itsoriginal position out of contact with either switch 29 or switch 30 andthe or each motor is de-energised and movement of the mould is stopped.

Regular changes in electrode diameter cause all probes 20 to pivot inequal amounts and the rods 27 to move upwardlyor downwardly within thebearings 28.

Whilst the invention has been described with reference to the melting ofelectrodes of circular crosssection, the invention is equally applicableto processes in which electrodes of square, rectangular or othercross-section are employed.

I claim:

1. A process for the refining of metals in which a consumable electrodeof the metal to be refined is melted in a vessel, which processcomprises detecting changes in the clearance between opposed surfaces ofthe consumable electrode and the vessel inner wall by means of at leastthree pivotally mounted probes which bear against the adjacent surfaceof the electrode and which pivot to actuate control means operable tocause drive means to impart relative horizontal movement between theelectrode and the vessel to restore the clearance.

2. A process according to claim 1 wherein two or more pairs of pivotallymounted probes are provided,

activated by movement of the electrode relative to the mould in adirection which reduces the clearance therebetween to a value less thanthe predetermined minimum clearance, producing on activation of at leastone of said probes a signal indicative of the direction of said relativemovement, and using said signal to actuate control means to effectrelative horizontal movement between the electrode and the mould toreturn the electrode and mould to their predetermined spacedrelationship.

2. A process according to claim 1 wherein two or more pairs of pivotallymounted probes are provided, the probes of each pair being positioned tobear against opposed surfaces of the electrode.
 3. In a process for therefining of metals in which a consumable electrode of the metal to berefined is positioned in a predetermined spaced relationship to themould, the steps of detecting relative movement in a horizontaldirection between the electrode and mould by means of at least threeprobes which are spaced around and extend inwardly from the vessel innerwall to define a predetermined minimum clearance between the vesselinner wall and the electrode and which are activated by movement of theelectrode relative to the mould in a direction which reduces theclearance therebetween to a value less than the predetermined minimumclearance, producing on activation of at least one of said probes asignal indicative of the direction of said relative movement, and usingsaid signal to actuate control means to effect relative horizontalmovement between the electrode and the mould to return the electrode andmould to their predetermined spaced relationship.